The packaging and labeling arts have long used heat shrinkable plastic tubing, typically polyvinylchloride (PVC) for the purposes of quickly and efficiently banding together multiples, groups or combinations of products and/or in labeling products of any shape or securing promotional premiums or the like to articles. The heat shrinkable bands or labels employed heretofore have been manufactured primarily as "seamless" tubing, by pneumatically expanding a continuously formed hollow cylinder of PVC or polyethylene and then permitting the expanded cylinder to be cooled. The resulting tubing has a "memory" and will shrink radially and longitudinally upon the subsequent application of heat thereto. Alternatively, heat shrinkable tubing has been formed by taking flat sheets or webs of heat shrinkable PVC or other heat shrinkable material and forming the same into a "tube" or band folding the sheets or webs and connecting the free ends by a sealed seam or joint. The resulting tubing is "seamed".
Disclosed herein is a new and improved method of continuously forming a heat shrinkable packaging medium having a new and improved integral tear strip. The method generally comprises the steps of supporting a roll of flat folded heat shrinkable seamless tubing material for controlled unwinding; directing a web of tubing drawn from the roll toward a sealing station; forming perforations along one edge of the tubing; directing the perforated tube to an ultrasonic welding station; applying ultrasonic welding energy exteriorly and longitudinally of the tube while pinching the walls thereof between an ultrasonic horn means bearing against lower exterior surfaces of the tubing proximate to the perforations and a sealing bar means bearing against the upper surfaces of the tubing, thereby welding said walls into a permanent tear strip; and advancing the welded tube with the integral tear strip to a rewind station.
The resulting heat shrinkable tubular element comprises a shrinkable packaging sleeve having juxtaposed top and bottom walls, the sides of which are the parallel fold lines of tubing. The ultrasonically established weld permanently joining the top and bottom walls adjacent to the perforations defines an easy-opening tear strip which, when subsequently heat shrunk, forms a readily graspable element which projects from the periphery of the object about which the sleeve is placed.
For a better appreciation of the principles of the present invention and a more complete understanding of its attendant advantages, reference should be made to the following detailed description of the invention taken in conjunction with the accompanying drawings.